Primer composition

ABSTRACT

A primer composition comprises (I) a modified copolymer obtainable by addition of a polar group represented by the following formula (1) or (2) to at least one (co)polymer selected from an olefin (co)polymer, a halogenated olefin (co)polymer, a styrene/conjugated diene/styrene tri-block copolymer or its hydrogenated product and a halogenated styrene/conjugated diene/styrene tri-block copolymer or its hydrogenated product, wherein the modified copolymer contains the polar group in an amount of from 1×10 −3  to 250×10 −3  mol based on 100 g of the modified copolymer, and (II) an organic solvent;                    
     in the formulas (1) and (2), R 1  is hydrogen or an alkyl group of 1 to 6 carbon atoms, R 2  is an alkylene group of 1 to 6 carbon atoms and n is an integer of 1 to 20. 
     The present invention can provide the primer composition having excellent adhesion between polyolefin molded articles or steel plates, which are substrates (coated objects), and various materials (coating materials, adhesives and the like) and further having excellent storage stability and pigment-loading properties.

This application is the national phase under 35 U.S.C. §371 of PCTInternational Application No. PCT/JP01/05797 which has an Internationalfiling date of Jul. 4, 2001, which designated the United States ofAmerica.

FIELD OF THE INVENTION

The present invention relates to a primer composition for coating andbonding molded articles of polyolefins such as polypropylene or thelike, particularly, relates to a primer composition showing excellentstorage stability for storing under mixing with water-containingsubstances such as pigments, water or moisture.

BACKGROUND OF THE INVENTION

Conventionally, molded articles of polyolefins such as polypropylenehave been enhanced in their values by application of paints or formationof resin layers other than polyolefin to the surfaces thereof. However,polyolefins generally have a small polarity and inferior adhesion togeneral coating materials or other resins. On this account, the adhesionof a polyolefin molded article to coating materials or the like hasconventionally been improved by enhancing the surface polarity thereofwith treatment of the polyolefin molded article surface using chromicacid, flame, corona, plasma or solvents.

These methods, however, have defects that they require complicatedtreatments, are accompanied with danger of using corrosive chemicals andalso require strict process control for obtaining stable adhesiveness.

The present applicant discloses, in JP-B-62-21027/1987 andJP-B-59-42693/1984, that using, as a primer (surface treating agent), asolution of dissolving a graft copolymer obtainable by graftco-polymerization of a propylene/ethylene copolymer orethylene/propylene copolymer with maleic anhydride in an organicsolvent, the adhesion between a coated object (for example, polyolefinmolded articles such as polypropylene molded articles) and a coatingmaterial or adhesive is improved to attain good adhesion.

These primer compositions can exert good adhesion between a substrate(coated object) and a coating material or adhesive. However, when theyare kept for a long time under water or moisture contact conditions, theproblem of increasing their viscosities will be induced, and whenwater-containing products such as pigments are added to them, foreignmatters will be produced or increasing their viscosities will beinduced.

In order to solve these problems, the present applicant proposed, inJP-B-61-11250/1986, a primer composition (surface treating agent)prepared by dissolving a modified ethylene/propylene copolymer, which isobtainable by grafting a mono-olefin dicarboxylic acid monoalkyl ester,in an organic solvent.

The above problems for the primer compositions are solved, however, theyare found to have a defect of lowering the adhesion with a specificcoating material or a specific adhesive.

Therefore, the advent of primer compositions having excellent adhesionbetween a polyolefin molded article, which is a substrate (coatedobject) and various materials (coating materials, adhesives or thelike), and excellent storage stability and pigment-loading propertieshas been desired.

The present invention is intended to solve the problems associated withthe prior art as mentioned above. It is an object of the invention toprovide a primer composition having excellent adhesion between apolyolefin molded article, which is a substrate (coated object) andvarious materials (coating materials, adhesives or the like), andexcellent storage stability and pigment-loading properties.

DISCLOSURE OF THE INVENTION

The primer composition of the present invention comprises:

(I) a modified copolymer obtainable by addition of a polar grouprepresented by the following formula (1) or (2) to at least one(co)polymer selected from

(A) an olefin (co)polymer,

(B) a halogenated olefin (co)polymer

(C) a styrene/conjugated diene/styrene tri-block copolymer or itshydrogenated product and

(D) a halogenated styrene/conjugated diene/styrene tri-block copolymeror its hydrogenated product, and

(II) an organic solvent,

wherein the modified copolymer contains the polar group in an amount offrom 1×10⁻³ to 250×10⁻³ mol based on 100 g of the modified copolymer,

in the formulas (1) and (2), R¹ is hydrogen or an alkyl group of 1 to 6carbon atoms, R² is an alkylene group of 1 to 6 carbon atoms and n is aninteger of 1 to 20.

The primer composition of the present invention preferably has a contentof the organic solvent (II) of from 100 to 4000 parts by weight based on100 parts by weight of the modified copolymer (I).

BEST MODE OF CARRYING OUT THE INVENTION

The primer composition of the present invention will be described indetail hereinafter.

The primer composition of the present invention comprises (I) thespecific modified copolymer and (II) the organic solvent.

Modified Copolymer (I)

The modified copolymer (I) used for the invention is a graft-modifiedproduct of at least one (co)polymer selected from (A) an olefin(co)polymer, (B) a halogenated olefin (co)polymer, (C) astyrene/conjugated diene/styrene tri-block copolymer or its hydrogenatedproduct and (D) a halogenated styrene/conjugated diene/styrene tri-blockcopolymer or its hydrogenated product, and has the specific polar group.

[(A) Olefin (Co)polymer]

The olefin (co)polymer (A) used for the invention is a homopolymer of atleast one α-olefin or a copolymer comprising at least two α-olefins.

Exemplary α-olefins are α-olefins of 2 to 20 carbon atoms, preferably 2to 8 carbon atoms, and specifically may include ethylene, propylene,1-butene, 4-methyl-1-pentene, 3-methyl-1-pentene, 1-hexene,2-methyl-1-pentene, 1-heptene and 1-octene.

Among of the α-olefin (co)polymers, it is preferred to use apropylene/ethylene copolymer, propylene/1-butene copolymer andethylene/1-octene copolymer as the olefin (co)polymer (A).

The intrinsic viscosity [η] as measured in decalin at 135° C. of theolefin (co)polymer (A) is desirably in the range of 0.05 to 5.0 dl/g,preferably 0.1 to 2.0 dl/g.

[(B) Halogenated Olefin (Co)polymer]

The olefin (co)polymers for the halogenated olefin (co)polymer (B) usedin the invention may include, for example, the above-described olefin(co)polymers (A).

Examples of the halogen used in the halogenation of the olefin (co)polymer (A) may include fluorine, chlorine and bromine.

The degree of halogenation varies depending on the kinds of substrate tobe subjected to primer treatment and coating objects such as coatingmaterials and adhesives, and further, is desirably in the range ofgenerally 5 to 40% by weight, preferably 10 to 30% by weight based on100% by weight of the olefin (co) polymer before the halogenation.

[(C) Styrene/Conjugated Diene/Styrene Tri-Block Copolymer or ItsHydrogenated Product]

The styrene/conjugated diene/styrene tri-block copolymer or itshydrogenated product (C) used in the present invention is a copolymerwhich comprises a polymer block (S) having at least one recurringstructural unit derived from styrene in its molecule and a conjugateddiene polymer block (Di) having at least one recurring structural unitderived from conjugated diene in its molecule and has, for example, astructure represented by the following formula:

—(S-Di-S)_(n)—

in the formula, n is an integer of 1 or more.

Examples of the conjugated diene for the styrene/conjugateddiene/styrene tri-block copolymer may include isoprene and butadiene.The tri-block copolymer may contain the conjugated diene singly or incombination with two or more.

Preferably, the styrene content of the tri-block copolymer is generally10 to 55% by weight, particularly 15 to 50% by weight.

The styrene/conjugated diene/styrene tri-block copolymer or itshydrogenated product used in the invention has a number averagemolecular weight (Mn) of preferably from 1×10⁴ to 18×10⁴, morepreferably 1.5×10⁴ to 12×10⁴. In the present invention, the numberaverage molecular weight (Mn) is determined using tetrahydrofurane as asolvent at 40° C. by gel permeation chromatography (GPC).

[(D) Halogenated Styrene/Conjugated Diene/Styrene Tri-Block Copolymer orits Hydrogenated Product]

The styrene/conjugated diene/styrene tri-block copolymer or itshydrogenated product for the halogenated styrene/conjugateddiene/styrene tri-block copolymer or its hydrogenated product (D) usedin the invention is, for example, the styrene/conjugated diene/styrenetri-block copolymer or its hydrogenated product (C).

Examples of the halogen used for halogenation of the styrene/conjugateddiene/styrene tri-block copolymer or its hydrogenated product (C) mayinclude fluorine, chlorine and bromine.

The degree of halogenation varies depending on the kinds of substrate tobe subjected to primer treatment and coating objects such as coatingmaterials and adhesives, and further, is desirably in the range ofgenerally 5 to 40% by weight, preferably 10 to 30% by weight based on100% by weight of the styrene/conjugated diene/styrene tri-blockcopolymer or its hydrogenated product before the halogenation.

[Polar Group]

The polar group which is added to the (co)polymer as described above isrepresented by the following formula (1) or (2).

In the formulas (1) and (2), R¹ is hydrogen or an alkyl group of 1 to 6carbon atoms, R² is an alkylene group of 1 to 6 carbon atoms and n is aninteger of 1 to 20.

Examples of the alkyl group of 1 to 6 carbon atoms for R¹ may includemethyl, ethyl, propyl, isopropyl, butyl, isobutyl, s-butyl, t-butyl,pentyl, isopentyl, t-pentyl, neo-pentyl, 1-methylbutyl, hexyl, andisohexyl groups.

Examples of the alkylene group of 1 to 6 carbon atoms for R² may includemethylene, ethylene, propylene, trimethylene, butylene, pentene andhexene groups.

The process for adding the polar group of the formula (1) to the above(co)polymer may include a process of conducting graft copolymerizationof a compound having the polar group of the formula (1) to the(co)polymer directly. It is, further, preferred to employ a process ofpreviously conducting graft-copolymerization of an unsaturateddicarboxylic acid represented by the formula (a) or (b) or its acidanhydride to the (co)polymer and then allowing to react with a diolcompound represented by the formula (c) in view of preparing themodified copolymer (I) in a high yield.

Preferable examples of the diol compound may include glycols such asethylene glycol, diethylene glycol and triethylene glycol because ofhaving a high reactive efficiency.

Examples of the unsaturated dicarboxylic acid or its acid anhydride mayinclude maleic acid, fumaric acid, tetrahydrophthalic acid, itaconicacid, citraconic acid, crotonic acid, isocrotonic acid, norbornenedicarboxylic acid, tetra hydrophthalic acid andbicyclo[2,2,1]hepto-2-ene-5,6-dicarboxylic acid, or their acidanhydrides, and particularly, the acid anhydrides thereof are preferred.

These unsaturated dicarboxylic acids and their acid anhydrides may beused singly or in combination with two or more.

The process for graft copolymerization of at least one polar compoundselected from the above unsaturated dicarboxylic acids and their acidanhydrides on the above (co)polymer may include various processes.Examples thereof are:

(1) a process of conducting graft copolymerization by dissolving the(co)polymer in an organic solvent, adding the polar compound and aradical polymerization initiator and heating them with stirring;

(2) a process of conducting graft copolymerization by melting the(co)polymer with heating, adding the polar compound and a radicalpolymerization initiator to the resulting melt and stirring them;

(3) a process of conducting graft copolymerization by previously mixingthe (co)polymer with the polar compound and a radical polymerizationinitiator, feeding the resulting mixture to an extruder and kneading themixture with heating; and

(4) a process of conducting graft copolymerization by impregnating asolution prepared by dissolving the polar compound and a radicalpolymerization initiator in an organic solvent, into the (co)polymer,and then heating them to the highest temperature at which the(co)polymer is not dissolved.

The reaction temperature is not lower than 50° C., suitably from 80 to200° C., and the reaction time is about from 1 to 10 hours.

The reaction method may be any one of batch wise and continuous methods,and further the batch wise method is preferable in order to carry outthe graft copolymerization uniformly.

In conducting the polymerization using the radical polymerizationinitiator, the useful radical polymerization initiator may include anyone which can promote the reaction of the (co)polymer with the polarcompound, and particularly an organic peroxide and organic perester arepreferable.

Examples of the organic peroxide may include benzoyl peroxide, dichlorobenzoyl peroxide, dicumyl peroxide, di-tert-butyl peroxide,2,5-dimethyl-2,5-di(peroxy benzoate)hexyne-3,1,4-bis(tert-butylperoxyisopropyl)benzene, lauroyl peroxide,2,5-dimethyl-2,5-di(tert-butylperoxy)hexyne-3 and2,5-diemthyl-2,5-di(tert-butyl peroxide)hexane.

Examples of the organic perester may include tert-butylperacetate,tert-butylbenzoate, tert-butyl perphenyl acetate, tert-butylperisobutylate, tert-butyl per-sec-octoate, tert-butyl perpivalate,cumyl perpivalate and tert-butyl perdiethyl acetate.

Usable examples of the radical polymerization initiator may include azocompounds such as azobisisobutyronitrile, and dimethylazoisobutyronitrile.

Among these compounds, dialkyl peroxides such as dicumyl peroxide,di-tert-butyl peroxide, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexyne-3,2,5-dimethyl-2,5-di(tert-butyl peroxy)hexane, and1,4-bis(tert-butyl peroxy isopropyl)benzene are preferable.

It is preferred to use the radical polymerization initiator in an amountof about 0.001 to 10 parts by weight based on 100 parts by weight of the(co)polymer.

The modified copolymer (I) used in the invention is obtainable byallowing the acid modified (co)polymer thus prepared to react with theabove diol compound.

This reaction may be carried out in the same way as the above acidmodification reaction (graft copolymerization reaction) with or withoutusing the radical polymerization initiator.

The modified copolymer (I) having the polar group of the formula (1) canbe prepared by the above process, and contains the polar group of theformula (1) in an amount of from 1×10⁻³ to 250×10⁻³ mol based on 100 gof the modified copolymer (I) and preferably 10×10⁻³ to 100×10⁻³ molwith the view of improving the adhesion between molded articles andcoating materials or adhesives.

Organic Solvent (II)

In the preparation of the modified copolymer (I) used for the invention,the graft copolymerization reaction may be carried out in the presenceor absence of the organic solvent, as described in the above. In thepresent invention, a composition prepared by dissolving the modifiedcopolymer (I) in the organic solvent (II) is used as the primercomposition.

Accordingly, when the modified copolymer (I) is prepared by graftcopolymerization in the organic solvent, it may be used as the primercomposition of the invention as it is or with the same or other kind ofthe organic solvent (II) newly added.

On the other hand, when the modified copolymer (I) is prepared by graftcopolymerization in the absence of the organic solvent, the modifiedcopolymer (I), which is a graft product, is dissolved by newly addingthe organic solvent (II) and then used as the primer composition of theinvention.

The organic solvent (II) for forming the primer composition of theinvention, which is added in the graft copolymerization reaction orafter the reaction, is not particularly limited, and examples thereofmay include:

aromatic hydrocarbons such as benzene, toluene or xylene;

aliphatic hydrocarbons such as hexane, heptane, octane or decane;

alicyclic hydrocarbons such as cyclohexane, cyclohexene ormethylcyclohexane;

alcohols such as methanol, ethanol, isopropyl alcohol, butanol,pentanol, hexanol, propanediol or phenol;

ketones such as acetone, methyl isobutyl ketone, methyl ethyl ketone,pentanone, hexanone, isophorone or acetophenone;

cellosolves such as methyl cellosolve or ethyl cellosolve;

esters such as methyl acetate, ethyl acetate, butyl acetate, methylpropionate or butyl formate; and

halogenated hydrocarbons such as trichloroethylene, dichloroethylene orchlorobenzene.

Among these, aromatic hydrocarbons, aliphatic hydrocarbons and ketonesare preferable. These organic solvents (II) may be used singly or incombination with two or more.

In the present invention, the desirable content of the organic solvents(II) is preferably from 100 to 4000 parts by weight, more preferably 200to 2000 parts by weight based on 100 parts by weight of the modifiedcopolymer (I).

Primer Composition

The primer composition of the invention comprises the modified copolymer(I) and the organic solvent (II), as described in the above, and isessentially used as a surface treating agent for plastic moldedarticles.

The surface of a molded article made of olefin (co)polymers or other(co)polymers is coated with the primer composition of the presentinvention and dried, and thereafter the primer composition coatedsurface is coated with a coating material, and thereby the adhesionbetween the molded article and the coating material can be improved.Similarly, the primer composition coated surface is coated with anadhesive, and thereby the adhesion between the molded article and theadhesive can be improved.

Preferable examples of the above molded article may include moldedarticles made of polyolefins such as high-pressure polyethylene,moderate or low-pressure polyethylene, polypropylene,poly-4-methyl-1-pentene or polystyrene, and molded articles made ofolefin copolymers such as ethylene/propylene copolymer, ethylene/butenecopolymer or propylene/butene copolymer.

Further, in addition to the above polyolefins and olefin copolymers, theprimer composition of the invention can be used in molded articles madeof polypropylene and synthetic rubber, molded articles for automobilesmade of polyamide resin, unsaturated polyester resin, polybutyleneterephthalate resin or polycarbonate resin, and surface treatment forsteel plates or electrodeposition-treated steel plates.

Further, prior to the application of coating materials, primersexcluding the primer composition of the present invention and adhesiveswhich essentially comprise polyurethane resin, aliphatic acid modifiedpolyester resin, oil-free polyester resin, melamine resin or epoxy resinto the surfaces of molded articles, under-coat with the primercomposition of the invention is previously conducted, thereby improvingthe adhesion between the molded articles and coating materials, primersand adhesives, and forming coating films (coating material-coated films,primer films and adhesive films) having excellent clearness and impactresistance at low temperatures.

Particularly, application of undercoating with the primer composition ofthe present invention is suitable for improving the adhesiveness ofcoating materials to the surfaces of molded articles. Applicable moldedarticles are molded articles made of polyolefins such as polypropyleneor the like, car bumpers made of polypropylene and synthetic rubber,molded articles of instrument panels, SMC (sheet molding compound)molded articles obtainable by using unsaturated polyester resin, epoxyresin etc, R-RIM (Reinforced reaction injection molding) molded articlesof polyurethane resin, glass fiber-reinforced polyamide resin moldedarticles, polyurethane resin molded articles and cationelectrodeposition-coated steel plates.

The molded articles on which the primer composition of the presentinvention is applied, may be prepared by molding the above various(co)polymers or resins by means of any known molding methods includinginjection molding, compression molding, blow molding, extrusion moldingand rotational molding.

Application of the primer composition of the invention on even moldedarticles mixed with pigments or inorganic fillers such as talc, zincwhite, glass fiber, titanium white or magnesium sulfate can form aprimer coating film having excellent adhesion.

Further, the molded articles to which the primer composition of theinvention is applicable may contain various additives such asstabilizers, ultraviolet light absorber or hydrochloric acid-absorbentin addition to the above inorganic fillers and pigments.

The process for application of the primer composition of the inventionon the surfaces of molded articles is not particularly limited. Theapplication can be conducted by known processes such as bar coater, rollcoater, dipping and spraying coatings.

The application of the primer composition of the invention on moldedarticles is conducted at ordinary temperatures. The wet coating film ofthe primer composition applied on the surfaces of molded articles isdried by appropriate processes such as air-drying or forced drying withheat to thereby form a hardened coating film (primer coating film) ofthe primer composition of the present invention on the surface of themolded article.

As described in the above, the primer composition of the presentinvention is applied on the surface of a molded article and dried, andthereafter a coating material and an adhesive can be applied on thesurface of the molded article by any one of processes of bar coater,roll coater, dipping, spraying and brushing coatings.

The employable coating material is not particularly limited.Particularly, in the case of application using a solvent typethermoplastic acrylic resin-coating material, solvent type thermosettingacrylic resin coating material, acryl modified alkyd resin coatingmaterial, epoxy resin coating material, polyurethane resin coatingmaterial and melamine resin coating material, the use of the primercomposition of the present invention can develop good adhesion.

Further, the employable adhesive is not particularly limited. Employableexamples thereof are urea resin adhesive, melamine resin adhesive,acrylic resin adhesive, epoxy resin adhesive, urethane resin adhesive,phenol resin adhesive, vinyl acetate solvent type adhesive, syntheticrubber solvent type adhesive, chloroprene solvent type adhesive, naturalrubber solvent type adhesive, vinyl acetate resin emulsion typeadhesive, vinyl acetate copolymer resin emulsion type adhesive, EVAemulsion type adhesive, acrylic resin emulsion type adhesive, urethaneresin emulsion type adhesive and epoxy resin emulsion type adhesive.

The primer composition of the present invention is applicable forwidespread uses with making the best use of its properties in additionto the above use of the primer for the molded articles. For example, itis applicable for uses such as additives for adhesives, additives forcoating materials and binders for glass fiber.

EFFECT OF THE INVENTION

The present invention can provide the primer composition havingexcellent adhesion between polyolefin molded articles or steel plates,which are substrates (coated objects), and various materials (coatingmaterials, adhesives or the like), and further having excellent storagestability and pigment-loading properties.

EXAMPLE

Hereinafter, the present invention is further described with referenceto the following non-limiting examples.

In the examples and comparative examples, the storage stability test ofthe primer composition and physical property test of the coating filmwere carried out in accordance with the following methods.

[1] Storage Stability Test

The primer composition was regulated with toluene to have a solidconcentration of 8.5% by weight and 1000 ppm of water was added to themand stirred. The appearance and viscosity (Ford cup viscosity No. 4) ofthe resulting mixture were measured every 10 days until 30 days.

[2] Cross Cut Test

A specimen having cross cuts was prepared in accordance with a methodfor cross cut test as defined in JIS K5400, and a cello tape (Trade namemanufactured by Nichiban Co.) was adhered to the cross cuts of thespecimen. Thereafter the tape was drawn quickly at a direction of 90° topeel it off and the number of cross cuts from which the coating film wasnot peeled off was counted within 100 cross cuts and was taken as anindication of the adhesion of the coating film.

[3] Peeling Strength Test

A coating film was formed on a substrate and a cut having a 1 cm widthwas formed with a cutter until the edge of the cutter reached to thesubstrate, then the edge of the coating film was released. Thereafter,the released edge of the coating film was pulled at a direction of 180°C. at a rate of 50 mm/min until the coating film was peeled off and thenpeeling strength [g/cm] was measured.

Example 1

112.5 g of a propylene/ethylene copolymer having an ethylene content of40 mol % and an intrinsic viscosity [η] as measured in decalin at 135°C. of 2.0 dl/g and 392 g of toluene were charged to a 1 L volumeautoclave with a stirrer, heated to 145° C. and stirred to dissolve themcompletely.

Next, while this solution was kept at 145° C. with stirring, 10.4 g ofmaleic anhydride and 3.6 g of di-tert-butylperoxide were added dropwiserespectively to the solution over 4 hr. After completion of theaddition, the post-reaction was carried out with stirring the mixture at145° C. for 2 hr to obtain a reaction solution (a) including a maleicanhydride-grafted copolymer.

After completion of the reaction, the solution was cooled to roomtemperature and acetone was added to the solution to deposit the maleicanhydride-grafted copolymer. The deposited maleic anhydride-graftedcopolymer was washed with acetone repeatedly and then dried, and aspecimen of the maleic anhydride-grafted copolymer was prepared.

The resulting specimen of the maleic anhydride-grafted copolymer has anintrinsic viscosity [η] as measured in decalin at 135° C. of 1.1 dl/gand a grafted amount of maleic anhydride of 46×10⁻³ mol based on 100 gof the grated copolymer.

In the next place, to the reaction solution (a), 4.4 g of diethyleneglycol (available by Mitsui Chemicals Inc.) (equimolar based on themaleic anhydride charged) was added, heated to 165° C. and allowed toreact for 5 hr to obtain a specimen of a modified copolymer.

As a result of IR analysis of the resulting specimen of the modifiedcopolymer, the degree of the reaction of diethylene glycol was 80% andthe content of a polar group represented by the following formulacorresponding to the formula (1) was 37×10⁻³ mol per 100 g of themodified copolymer.

Subsequently, 42.5 g of this modified copolymer was dissolved in 457.5 gof toluene, which is an organic solvent, to prepare a primer composition(solution).

Then, a solution prepared by adding 30 parts of xylene to 100 parts ofthe primer composition was applied with spraying on a polypropylenesquare plate whose surface had been cleaned with isopropyl alcohol(polypropylene Trade Name X708, manufactured by Grand Polymer Co.) so asto be a dried coating film thickness of 3 μm and dried naturally to forma primer coating film on the square plate surface.

In the next place, on the primer coating film, a facing material (TradeName R-278 (white) two-component urethane resin coating material,manufactured by Nippon Bee Chemical Co. Ltd.) was applied to form acoating film having a dried coating film thickness of 30 μm. The coatedplate was allowed to stand at room temperature for 10 min, then put intoan air oven heated at 100° C. and baked for 30 min to prepare a specimenfor the cross cut test. The cross cut test was carried out using thespecimen in accordance with the above method.

Similarly, a specimen having a dried facing material-coated filmthickness of 100 μm for the peeling test was prepared in the same mannerand the peeling test thereof was conducted in accordance with the abovemethod.

The results are shown in Table 3.

Further, with reference to the primer composition (solution), thestorage stability test was conducted in accordance with the abovemethod. The results of observing the appearance of the primercomposition are shown in Table 1, and the change of the viscosity withtime is shown in Table 2.

Comparative Example 1

5.2 g of methanol (4 times by mol based on the amount of maleicanhydride added dropwise in the reaction) was added to the reactionsolution (a) including the maleic anhydride-grafted copolymersynthesized in Example 1, heated to 165° C. and reacted for 5 hr. Afterthe reaction, the solution was cooled to room temperature to prepare aspecimen of a modified copolymer.

As a result of IR analysis of the resulting specimen modified copolymer,the degree of the esterification with methanol was 95% (the degree ofthe esterification was taken as 200% when all maleic anhydride wasdimethyl ester).

Then, 42.5 g of the modified copolymer was dissolved in 457.5 g oftoluene being an organic solvent to prepare a primer composition(solution).

Using the primer composition, the coating test including the cross cuttest and the peeling test, and the storage stability test were conductedin the same manner as in Example 1. The results are shown in Tables 1, 2and 3.

Comparative Example 2

Using the reaction solution (a) including the maleic anhydride-graftedcopolymer synthesized in Example 1, as a primer composition, the coatingtest including the cross cut test and the peeling test, and the storagestability test were conducted in the same manner as in Example 1. Theresults are shown in Tables 1, 2 and 3.

TABLE 1 Storage Stability Appearance of Primer composition After 10 daysAfter 20 days After 30 days Example 1 Transparent TransparentTransparent Compara. Ex. 1 Transparent Transparent Transparent Compara.Ex. 2 Opaque Opaque Opaque

TABLE 2 Storage Stability Viscosity Change of Primer composition withtime Initial Viscosity Viscosity Viscosity viscosity after 10 after 20after 30 [sec] days [sec] days [sec] days [sec] Example 1 20 20 20 20Compara. Ex. 1 18 18 18 19 Compara. Ex. 2 17 20 36 48

TABLE 3 Coating film properties Cross cut test Number of cross cuts withPeeling strength coating film remained/100 [g/cm] Example 1 100/100 1050Compara. Ex. 1 100/100 640 Compara. Ex. 2 100/100 1000

What is claimed is:
 1. A primer composition comprising: (I) a modifiedcopolymer obtained by addition of a polar group represented by thefollowing formula (1) or (2)

 wherein in the formulas (1) and (2), R¹ is hydrogen or an alkyl groupof 1 to 6 carbon atoms, to at least one copolymer selected from thegroup consisting of (A) an olefin copolymer, (B) a halogenated olefincopolymer (C) a styrene/conjugated diene/styrene tri-block copolymer orits hydrogenated product and (D) a halogenated styrene/conjugateddiene/styrene tri-block copolymer or its hydrogenated product, whereinthe modified copolymer contains the polar group in an amount of from1×10⁻³ to 250×10⁻³ mol based on 100 g of the modified copolymer, and(II) an organic solvent.
 2. The primer composition according to claim 1,wherein the modified copolymer (I) is obtained by modifying a maleicanhydric-grafted copolymer with diethylene glycol.
 3. The primercomposition according to claim 2, wherein the maleic anhydride-graftedcopolymer is maleic anhydride-grafted propylene/ethylene copolymer. 4.The primer composition according to claim 1 which has a content of theorganic solvent (II) of from 100 to 4000 parts by weight based on 100parts by weight of the modified copolymer (I).